In recent years, electric equipment such as voice equipment and visual equipment has become small, light and thin. Especially, in the OA (Office Automation) field, a personal computer has been miniaturized, e.g., from a desktop type to a notebook type, and a memory card has been developed. Furthermore, the aforementioned electric equipment is designed to be connected with a cellular phone.
As electronic apparatus has become small and light, a secondary battery and/or capacitor are required to have an improved performance and lightweight. To cope with the aforementioned requests, a secondary battery has been changed from a conventional lead storage battery to a nickel-cadmium battery or a lithium battery having high energy density. Recently, a lithium-ion secondary battery and a nickel-hydrogen secondary battery have become popular. Thus, the development in this field has been made quickly. Furthermore, an electrical double layer condenser, which can be used as a power supply of a hybrid car because of its high volume energy density, durable charge-and-discharge performance, is being put in practical use.
A secondary storage battery is required to be charged and discharged repeatedly. In this secondary storage battery, if moisture is mixed therein at the time charging, hydrolysis of the electrolyte and/or organic solvent may occur. Furthermore, if oxygen and/or moisture contained in the ambient air are introduced into the battery, deterioration and/or decomposition of the positive active material, negative electrode active material and/or conductive polymer may occur. Accordingly, the casing for an electronic component is required to be strictly sealed. The similar requirement is applied to an electronic component, such as an electric double layer condenser containing non-basin electrolyte.
To cope with such requirements of lightweight and sealing, it has been proposed that a laminated member laminating a thermoplastic resin film and an aluminum foil is used as a casing material for an electronic component.
For example, Japanese Unexamined Laid-open Patent Publication S59-173944 (hereinafter referred to as “JP59-173944”) proposes a casing material for an electronic component. In the casing material, an aluminum thin foil is covered by a resin film, or an aluminum thin foil is sandwiched between resin films.
Japanese Unexamined Laid-open Patent Publication H8-83596 (hereinafter referred to as “JP8-83596”) proposes to utilize a lamination of polyethylene film/aluminum film/polyethylene film as a casing material for a thin card-shaped battery.
Japanese Unexamined Laid-open Patent Publication H9-213285 (hereinafter referred to as “JP9-213285′) proposes a casing material for an electronic component. The casing material has a multi-layer structure including at least one aluminum foil layer as an inner layer, and is formed into a cylindrical shape.
Japanese Unexamined Laid-open Patent Publication H10-157008 discloses a lamination film of polyethylene film/aluminum foil/hot melt layer/oriented polyester film. The publication also proposes to obtain a battery casing by thermally forming the laminated film. It is thought that a polyester film of copolymerization polyester having good thermoforming nature is preferably used as the aforementioned polyester film.
The aforementioned casing material as taught by JP59-173944 is formed by heat-pressing the end portions of a laminated member in which an aluminum foil having a thickness of 20 μm is sandwiched between polyethylene layers each having a thickness of 100 μm. The sealing is performed by heat-sealing the casing material. The casing material as taught by JP8-83596 is used as a casing material for a thin card-shaped electronic component. This casing material requires a large sealing portion (a heat sealed portion of external casing materials so as not to allow an invasion of air or moisture into an inside of battery) at an external peripheral portion of a power generation component of a battery. The ratio of the area and volume of the sealing portion to those of the entire battery is large, which impedes to increase the volume energy density of the battery.
Furthermore, according to the teaching of JP9-213285, the aluminum laminated member is formed into a cylindrical shape, then a power generation element is inserted into the cylindrically formed casing. Then, the lower and upper openings thereof are sealed by heat sealing or adhesive agent. Thus, the sealing area can be halved, and the volume energy density can be increased as compared with the aforementioned casing for a thin card-shaped electronic component. However, it must be said that the energy density is still inadequate.
The casing material as taught by JP10-157008 is to be subjected to heat forming. Since polyethylene is used as the materials of the inner film, it is difficult to satisfy the high temperature preservation examination (safety examination) of a battery requiring enough bonding strength at high temperature. In order to thermally forming it, it is preferable that the polyester film is a polymerization polyester film. On the other hand, since the oriented polyester film is inferior in adhesive performance, it thermally contracts at the time of thermoforming and cannot obtain sufficient bonding strength by a normal dry laminating adhesive. Thus, it is required to use hot-melt adhesive agent.
Furthermore, in place of the conventional aluminum casing with a vinyl chloride resin cover, a casing made of thermoplastic nylon lamination and aluminum materials (see Japanese Unexamined Laid-open Patent Publication No. H8-001857) or thermoplastic-polyester resin painted aluminum materials (see Japanese Unexamined Laid-open Patent Publication No. H9-275043) has become available. Thus, materials have been developed to decrease the weight and avoid the use of vinyl chloride resin.
Furthermore, another capacitor casing material has been proposed (see Japanese Unexamined Laid-open Patent Publication No. 2001-011658). The casing material includes an aluminum foil having a roughened surface, a chemical coating formed on the roughened surface and an organic resin covering formed on the coating.
In order to obtain a battery with high volume energy density that can be mounted in a miniaturized and thinned housing of an electronic apparatus, the casing of the battery is required to have a shape corresponding to the available space of the printed circuit board so that it can be fitted in the space without casing any dead space. In order to meet the aforementioned requirements, it is required that the casing is thin and has a sharp shape. Therefore, it is required that the aluminum foil laminated member is thinner, and can be formed into a desired shape sharply.
Judging from this point of view, since the aforementioned conventional material for a battery casing has, for example, a structure of polyethylene film (100 μm)/aluminum foil (20 μm)/polyethylene film (100 μL m) or polypropylene film (100 μm)/aluminum foil (20 μm)/polypropylene film (100 μm), the formability thereof is not satisfactory. Thus, the material cannot be used as it is.
Another proposal has been made. In this proposal, the casing for an electronic component has a structure of heat-resistant-resin oriented film/aluminum foil/polyolefine film, acid denaturized polyolefine film or ionomer resin film from the surface. This casing is thin and good in formability, and can dissolve almost all of the aforementioned problems. However, polyolefine, acid denaturized polyolefine or ionomer resin cannot assuredly prevent permeation of non-water-electrolysis liquid of a lithium battery, to thereby cause invasion of the aluminum foil. Furthermore, in case of using polyolefin resin, the adhesive property to the aluminum foil becomes insufficient. Thus, it was necessary to solve these problems. The similar problems can also be applied to a capacitor casing of a capacitor containing non-water-electrolysis.
It is an object of the present invention to provide a casing material for an electric component which is excellent in formability such as overhang forming and a deep drawing forming, excellent in strength, excellent in adhesive performance between an aluminum foil and a resin layer, excellent in impermeability of moisture, excellent in heat sealing performance, and will not be invaded by corrosive electrolyte.
It is another object of the present invention to provide a casing for an electric component.
It is still another object of the present invention to provide an electric component such as a storage battery with high volume energy density and a capacitor equipped with the aforementioned casing.